Compression strength reduction in composites with in-plane fiber waviness

The effect of fiber waviness, which develops during the processing and manufacture of fiber-reinforced composite structures, on compressive failure was investigated. Analytical and experimental evidence has shown that out-of-plane waviness (also referred to as layer or ply waviness) is a major contributing factor in compressive strength reduction; however, there is a paucity of data concerning the effects of in-plane waviness or wrinkling on the compressive response of composites. In this paper, we present data from a series of compression tests examining the effects of varying levels of in-plane fiber waviness. These tests used a novel combined shear/end loading compression test fixture (WTF combined loading compression test fixture) in order to ameliorate problems typically associated with pure end-loading (brooming and end-damage) and pure shear loading (tab debonding and high stress concentrations due to discontinuity stresses). The fixture performed adequately when testing wavy specimens, but we experienced repeated tab failures in the non-wavy specimens. The compression test results exhibit a distinct linear trend of decreasing compressive strength with increasing waviness severity as represented by the maximum off-axis angle of the wavy fibers. Optical microscopy revealed that kink bands, leading to catastrophic failure, initiate at the most severe fiber misorientation sites in the wavy regions.